The present invention relates to a diagnostic reagent of the agglutination type for the detection of Rheumatoid Factor, a process for its preparation, a method for its use in qualitatively and quantitatively detecting the presence of Rheumatoid Factor and a kit for such detection including such diagnostic reagent.
Rheumatoid Factor (RF) is an autoantibody directed against human or animal gamma-globulins, and especially against the Fc portion of human or animal IgG. The autoantibody itself may be one of several immunoglobulin classes (IgM, IgG and IgA), with the class most often detected in tests for RF being IgM due to its superior agglutination reactions due to its highly multivalent binding characteristics. The presence of RF in human serum is not necessarily indicative of rheumatoid arthritis since RF is present in normal populations and, increasingly, in patients having other diseases such as SLE, infectious mononucleosis and various viral infections. Existing reagents and kits for the detection of RF factor fall into two classes: Synthetic particles coated with IgG (generally by absorption) and erythrocytes (especially sheep erythrocytes) coated with antierythrocyte antibodies (generally of the IgG type), suspended in either instance in a storage-stable medium. The antibody-coated particle reagents have the disadvantage of less specificity than the erythrocyte type because of clumping in the absence of RF and because of agglutination (a positive test) with RF levels so low as to be found in the general population. The erythrocyte-type reagents and kits have the disadvantages of relatively large particles (5-8 micrometers) which can cause grainy suspensions even in the absence of RF in the sample, false positives due to antibodies to infectious mononucleosis in the serum analyzed (which cross-reacts with erythrocytes antigens) and generally low sensitivity (cannot detect the lowest levels of RF concentration in serum samples).